Insights Static Quiz -83, 2018 –Geography

Answer – a

• The velocity of waves changes asthey travel through materials with different The denser the material, the higheris the velocity. Their direction also changes asthey reflect or refract when coming acrossmaterials with different densities.
• S-waves arrive at the surface with some time These are called secondary waves. An
  important fact about S-waves is that they can travel only through solid materials. This characteristic of the S-waves is quite important. It has helped scientists to understand the structure of the interior of the earth. Reflection causes waves to rebound whereas refraction makes waves move in different directions.
• The surfacewaves are the last to report on seismograph.These waves are more destructive. They causedisplacement of rocks, and hence, the collapseof structures occurs.

Answer – a

• According to Wegener, all the continents formed a single continental mass and mega ocean surrounded the same. The super continent was named PANGAEA, which meant all earth. The mega-ocean was called PANTHALASSA, meaning all water. He argued that, around 200 million years ago, the super continent, Pangaea, began to split. Pangaea first broke into two large continental masses as Laurasia and Gondwanaland forming the northern and southern components respectively. Subse-quently, Laurasia and Gondwanaland continued to break into various
  smaller continents that exist today.
• The belt of ancient rocks of 2,000 million years from Brazil coast matches with those from western Africa. The earliest marine deposits along the coastline of South America and Africa are of the Jurassic age. This suggests that the ocean did not exist prior to that time. Marine deposits got formed on the coasts of each only after their separation.

Answer – d

• Tillite,sedimentary rock that consists of consolidated masses of unweathered blocks (large, angular, detached rock bodies) and glacial till (unsorted and unstratified rock material deposited by glacial ice) in a rock flour (matrix or paste of unweathered rock).
• The matrix, which comprisesa large percentage of the rock, usually is dark gray to greenish black in colour and consists of angular quartz and feldspar grains and rock fragments in a very fine-grained paste.
• The widespread tillites in the geologic record provide evidence of former intense and widespread glaciation; Recent tillites (less than 11,700 years old) can be directly connected with glaciation, and Pleistocene tillites (11,700 to 2,600,000 years old) can be convincingly related to glaciation, but many earlier till-like bodies cannot.
• Only tillites formed from the till deposited by continental ice sheets have a good chance of being preserved in the geologic record.

Answer – a

• The occurrence of rich placer deposits of gold in the Ghana coast and the absolute absence
  of source rock in the region is an amazing fact.
• The gold bearing veins are in Brazil and it is obvious that the gold deposits of the Ghana are derived from the Brazil plateau when the two continents lay side by side.

Answer – c